Install x4d-icons by entering the following commands in the terminal:
sudo apt update sudo apt install x4d-icons
Description:
X4D Icon set for various online document types
Icon set indicating document types and target versions of those specifications e.g. HTML, XHTML, CSS, MathML, etc. These are metric compatible & naming scheme compatible with other logos used for similar purposes.
Homepage: http://x4d.surgut.co.uk
Version: 1.2-1
Section: universe/graphics